Thread: Performance Engine
12-04-2006, 10:46 AM #1
MSX 1200 Big Bore
stroker1450; BASED ON BMEP THE 1350 MOTOR TRANSFER PORTS START FLOWING AT 3950 AND RUN OUT AT 7900.
THE 1350 REQUIRES 47.8 MM CARBS
THE NEW 1450 MOTOR WILL REQUIRE 50 MM AT 7500.
Last edited by ph2ocraft; 12-04-2006 at 03:18 PM.
12-05-2006, 11:32 PM #2
Jet Works Valve
From Art's web site.
The JETWORKS FLOW CONTROL VALVE provides improved throttle response and much quicker starts by drying out your water box at low rpm and idle speeds. Tests have shown an average acceleration improvement of 12 feet over a non-equipped model in the first 50 feet. The JETWORKS FLOW CONTROL VALVE allows unrestricted water flow to the stinger for better top speed. Yet it controls the amount of water at low speeds for better response. It also allows for an easier tuning of the carburetors. It does not interfere with normal engine or exhaust pipe cooling and is compatible with all electronic water injection systems.
In a race start situation, the craft is under a slight load while waiting the start, water fills up the water box and exhaust hoses. Upon sudden acceleration all of this water must be forced out quickly before full exhaust flow can occur. During this time the craft feels a slight hesitation and/or sluggishness, especially when the water box is mounted up front and has a rear exhaust.
The JETWORKS FLOW CONTROL VALVE improves response through turns when the throttle is let off for a split second. This dries out the water box while at the same time raising the water pressure slightly in the head pipe of the exhaust. This raised water pressure allows the water injection orifices and/or nozzles to work quicker and more effectively.
Two models are available. Both are adjustable. The STANDARD JETWORKS FLOW CONTROL VALVE is preset at 3.5p.s.i. and is adjustable by adding the supplied stainless steel shims to increase the spring tension. The PRO-SERIES JETWORKS FLOW CONTROL VALVE is externally adjustable by turning the outer housing by hand. Pressure can be tested with a pop off gauge. Both models feature a positive sealing viton on metal seals with a precision calibrated, variable rate spring. This allows for true water flow and pressure management of multiple water lines and dedicated cooling line applications.
For the guys that like a little more technical info.
What the valve does is stop the water flowing at idle and off idle speeds into the stinger where it builds up in the waterbox and exhaust hoses. Normally this water has to be forced out upon sudden acceleration in order to get full exhaust flow.
Here's how it works: At lower speeds, the water pressure in the water lines is low and the valve stops the flow to the stinger and raises the line pressure slightly. This improves response off the line and out of turns. At higher speeds, the water pressure rises and opens the valve to the stinger, allowing unrestricted flow of water. This creates a wall stream of water inside the stinger, thereby increasing the reflectability of the pipe in a similar way like a smaller diameter outlet would do.
What we mean by reflectability, by the way, is how the sonic wave is returned to the exhaust port with more energy, energy that would have escaped through the outlet. What's nice about the water stream is that it's variable; as the back pressure increases, it will push the water aside.
Last edited by K447; 04-15-2011 at 10:39 PM.
12-05-2006, 11:38 PM #3
12-05-2006, 11:41 PM #4
12-07-2006, 01:40 AM #5
12-08-2006, 02:24 AM #6
Pro 785 CDI conversion
Originally Posted by Ph2ocraft
I just verified the operation of the PRO CDI in the 93 750 today, it's perfect thus far, we'll see how it does once the triples are in.
I'm showing the working RPM's of the 97 PRO785 is 7500RPm and the limiter is set at 7800 RPM. It also has 32 degrees advance at 3,000 RPM so I think it's going to work VERY well with the triples on the 750 (I can't wait). We'll see if I'll run it on 92 or if I need a little VP110.
The PRO wires up much easier than I initially thought and goes as follows.
Blue/Red from CDI to Blue/Red from the stator
Red/White from CDI to Red/White from the stator
Green/Red from CDI to Green/White from Stator
White/Yellow from CDI to White/Yellow from Stator
Black/Yellow from CDI to Black/Yellow from Stop Switch
Black to Battery Ground
Black to Box Ground
I then seperated the wires from the coil pack and wired with individual pig tails as follows.
Black/Green from CDI to Black/White on PTO Coil
Black/Orange from CDI to Black/White on Center Coil
Black/White from CDI to Black/White on MAG Coil
Black from CDI to Black from Coil Grounds.
I capped off the following wires from the CDI as I have no use for the exhaust valve electrical signals
The last couple of wires
Tan from CDI to Tan from Temp sensor
Red/Purple from CDI to Red/purple at LR23
Yellow/Black from CDI to Yellow/Black from CDI (you read correctly)
12-22-2006, 12:01 PM #7
12-22-2006, 12:10 PM #8
01-15-2007, 11:11 PM #9
How To Determine Deck Height
This was copied from an unknown author. Thanks for the excellent info.
How do we determine Piston Deck Height??
1. Remove the cylinder head.
2. Grab your Dial Indicator and Magnetic Base (very accurate),Flat-Blade Depth Micrometer(accurate
3. Place piston at TRUE Top Dead Center (TDC) NOTE: Since every crank has dwell at TDC, determining TRUE TDC can be a bit tricky. Using a custom piston stop is the most accurate method for finding true TDC.
Now.. you know when you are at true TDC, so, all you have to do is measure the distance from the piston edge to the cylinder deck.
Please keep in mind... when measuring the deck height on a crowned piston, it is nearly impossible to get to the actual edge of the piston. This is because your measuring device does have mass and will hit the piston crown before it hits the actual edge. The finer the measuring device.. the more accurate the measurement. So.. if you are using the butt end of a dial caliper on a crowned piston, please keep in mind that this butt end is very wide and flat and will surely hit the crown way before the edge.
For pistons with a positive deck height, a step micrometer seems to be the most accurate tool for this measurement. It is nearly impossible to accurately measure positive deck without a step micrometer.If you can determine how far above the deck the center of the crown is at true TDC, you can subtract the known crown drop from this number to determine your deck height.
Deck Height is very important when determining engine parameters and designing combustion chambers, as there are often variances in cylinder castings, piston heights, connecting rod lengths, and base gasket thicknesses. ALL these things effect port timing and deck height.Deck height is a major player in determining the squish clearance of an engine.
Squish clearance is the distance from the edge of the piston, at TDC, to the outer edge of the combustion chamber's squish band. So, one can easily see how the deck height effects the squish clearance measurement.
You might be saying to yourself " So, what if I am off on my deck height measurement .008", how big of a deal can that be?"
Let's look at what .008" does to the compression ratio and volume of an engine.
Volume of a cylinder: PI * R^2 (radius = 1/2 bore) * H (Stroke)
Example, the 800 Rotax twin engine with an 82mm bore and a 76mm stroke. We will convert the .008" to mm so the numbers in the equation coincide. .008" = .2mm
Let's do the math: 3.14 * (82mm/2)^2 * .2mm = 1.05cc of volume change. So, what does 1.05cc of volume increase or decrease on this particular engine? Well.. 1.05cc equates to a 0.4 change in untrapped compression ratio. OK.. 0.4 change in untrapped compression ratio will change a 12:1 engine to a 12.4:1 or a 11.6:1 engine
So, you can see that the compression ratio is affected but what is also affected is the squish action within the head. Squish action is important in determining power characteristics of an engine. The squish band acts as a cooling layer to help cool the end gases as they are being rapidly compressed. By keeping these gases below their combustible temperature, one can prevent undesired combustion of these end gases in the squish band area. If these end gases are allowed to combust before the oncoming, spark initiated, flame front chooses to combust them, then you have detonation and engine damage.
The squish action also creates turbulence within the combustion chamber. This turbulence has a direct effect on the flame front speed so, in actuality, it affects ignition timing.
One important measurement for the squish action is the Maximum Squish Velocity (MSV). In short, this is the max velocity of the end gases as they are be compressed. It is actually a lot more complicated than that, but I will leave it at that for now. It is measured in meters/sec (m/s).
Let's take our above examples and see how squish velocity is changed by a small variance in squish clearance.
The first example showed a change in squish clearance of .2mm. This .2mm change in total squish clearance will increase the squish velocity in a 13.5:1 head by 7.4m/s if this .2mm is removed from the total squish clearance. If this .2mm is added to the total squish clearance, then the squish velocity is decreased by 5m/s.
Is there a benefit to having a smaller or larger Piston Deck Height??
The one that comes to mind first is in the cooling effects of the engine. For example,if the deck height is large in the cylinder, then there may be an argument for the end gases retaining more heat due to them being trapped in the cylinder vs. the head. One may argue that end gases trapped in the head portion of the squish band would be subject to the better cooling properties of the head. This would be a hard theory to prove, but it does have merit.
Can the Piston Deck Height be easily changed??
Below are several methods of altering deck height, which, as I have shown, also alters MANY other operating factors.
1. Changing base gasket thickness
2. Decking cylinder base
3. Decking cylinder top
4. Changing piston
5. Changing crank
6. Changing rod length
7. Changing stroke
8. Altering piston crown
01-19-2007, 08:55 PM #10
Domestic Pipe Mod 1050/1200
Last edited by ph2ocraft; 01-19-2007 at 08:59 PM.
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